US20070255136A1 - Method and system for measuring flow through a heart valve - Google Patents

Abstract

A system for presenting multiple parallel slices comprises a display for displaying ultrasound data comprising 3D Doppler data over time. A user interface defines a proximal plane and a distal plane within the ultrasound data that are parallel to one another. The proximal and distal planes define a region of interest (ROI). A signal processor automatically extracts at least two slices based on the ultrasound data within the ROI. The at least two slices are parallel with respect to each other and are displayed on the display.

Description

BACKGROUND OF THE INVENTION
• This invention relates generally to diagnostic ultrasound systems, and more particularly, to method and system for measuring flow through a heart valve.
• Diagnosing and assessing regurgitate flow jets within a patient's heart, such as mitral valve or tricuspid valve regurgitation or insufficiency, is challenging with currently available ultrasound systems. The flow patterns are often quite complex with time-varying geometries. Additionally, non-circular orifice areas pose a challenge to visualizing and measuring the flow through the actual orifice area.
• When accessing a condition such as Mitral Regurgitation, the size of the regurgitate flow jets may be currently described with the Vena Contracta. The Vena Contracts is defined as the narrowest central flow region of a jet and can be depicted using color flow Doppler. Currently, the proximal isovelocity surface area method (PISA) is used to quantify the size of the flow jet. This method is a planar measurement which makes the assumption that the flow convergence zone is circular and symmetric. Unfortunately, this is seldom the case, and may result in erroneous calculations.
• Therefore, a need exists for a method and system for improving the localization of the Vena Contracta to measure the flow through a heart valve. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.
BRIEF DESCRIPTION OF THE INVENTION
• In accordance with one embodiment, a system for presenting multiple parallel slices comprises a display for displaying ultrasound data comprising 3D Doppler data over time. A user interface defines a proximal plane and a distal plane within the ultrasound data that are parallel to one another. The proximal and distal planes define a region of interest (ROI). A signal processor automatically extracts at least two slices based on the ultrasound data within the ROI. The at least two slices are parallel with respect to each other and are displayed on the display.
• In accordance with another embodiment, a method for displaying multiple parallel slices comprises defining an ROI within a volume of data. The volume of data comprises volumetric color Doppler data over at least one cardiac cycle. At least two slices of ultrasound data are automatically displayed from within the ROI at a first time position. A first flow jet area is calculated on one of the at least two slices at the first time position.
• In accordance with another embodiment, a method for measuring a flow jet area over a portion of a cardiac cycle comprises defining an ROI within a volume of data comprising volumetric color Doppler data over at least one cardiac cycle. Multiple parallel slices of ultrasound data from within the ROI are displayed. A flow jet area is measured on a first slice at a first time position and a flow jet area on a second slice is measured at a second time position. The flow jet area is interpolated on the ultrasound data between the first and second time positions.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates a block diagram of an ultrasound system formed in accordance with an embodiment of the present invention.
• FIG. 2 illustrates a block diagram of an alternative ultrasound system formed in accordance with one embodiment of the present invention.
• FIG. 3 illustrates a method for locating and measuring a flow jet within the heart in accordance with an embodiment of the present invention.
• FIG. 4 illustrates ultrasound images displayed on the display in accordance with an embodiment of the present invention.
• FIG. 5 illustrates multiple parallel slices extracted from the ROI in accordance with an embodiment of the present invention.
• FIG. 6 illustrates an example of measuring the Vena Contracta area on one of the multiple parallel slices in accordance with an embodiment of the present invention.
• The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. The figures illustrate diagrams of the functional blocks of various embodiments. The functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or a block or random access memory, hard disk, or the like). Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed imaging software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 illustrates a block diagram of anultrasound system100. Theultrasound system100 includes atransmitter102 which drivestransducers104 within aprobe106 to emit pulsed ultrasonic signals into a body. A variety of geometries may be used. For example, theprobe106 may be used to acquire 2D, 3D , or 4D ultrasonic data, and may have further capabilities such as 3D beam steering. Other types ofprobes106 may be used. The ultrasonic signals are back-scattered from structures in the body, like blood cells or muscular tissue, to produce echoes which return to thetransducers104. The echoes are received by areceiver108. The received echoes are passed through abeamformer110, which performs beamforming and outputs an RF signal. The beamformer may also process 2D, 3D and 4D ultrasonic data. The RF signal then passes through anRF processor112. Alternatively, theRF processor112 may include a complex demodulator (not shown) that demodulates the RF signal to form IQ data pairs representative of the echo signals. The RF or IQ signal data may then be routed directly to RF/IQ buffer114 for temporary storage.
• Theultrasound system100 also includes asignal processor116 to process the acquired ultrasound information (i.e., RF signal data or IQ data pairs) and prepare frames of ultrasound information for display ondisplay118. Thesignal processor116 is adapted to perform one or more processing operations according to a plurality of selectable ultrasound modalities on the acquired ultrasound information. Acquired ultrasound information may be processed in real-time during a scanning session as the echo signals are received. Additionally or alternatively, the ultrasound information may be stored temporarily in RF/IQ buffer114 during a scanning session and processed in less than real-time in a live or off-line operation. Auser interface120 allows an operator to enter data, enter and change scanning parameters, access protocols, measure structures of interest, and the like. Theuser interface120 may be a rotating knob, switch, keyboard keys, mouse, touch screen, light pen, or any other interface device or method known in the art.
• Theultrasound system100 may continuously acquire ultrasound information at a frame rate that exceeds 50 frames per second—the approximate perception rate of the human eye. The acquired ultrasound information is displayed on thedisplay118. The ultrasound information may be displayed as B-mode images, M-mode, volumes of data (3D), volumes of data over time (4D), or other desired representation. Animage buffer122 is included for storing processed frames of acquired ultrasound information that are not scheduled to be displayed immediately. Preferably, theimage buffer122 is of sufficient capacity to store at least several seconds worth of frames of ultrasound information. The frames of ultrasound information are stored in a manner to facilitate retrieval thereof according to its order or time of acquisition. Theimage buffer122 may comprise any known data storage medium.
• FIG. 2 illustrates an alternative ultrasound system. The system includes aprobe10 connected to atransmitter12 and areceiver14. Theprobe10 transmits ultrasonic pulses and receives echoes from structures inside of a scannedultrasound volume16.Memory20 stores ultrasound data from thereceiver14 derived from the scannedultrasound volume16. Thevolume16 may be obtained by various techniques (e.g. 3D scanning, real-time 3D imaging or 4D scanning, volume scanning, 2D scanning with transducers having positioning sensors, freehand scanning using a Voxel correlation technique, 2D or matrix array transducers and the like).
• Theprobe10 may be moved, such as along a linear or arcuate path, while scanning a region of interest (ROI). At each linear or arcuate position, theprobe10 obtains scan planes18. The scan planes18 are collected for a thickness, such as from a group or set of adjacent scan planes18. The scan planes18 are stored in thememory20, and then passed to avolume scan converter42. In some embodiments, theprobe10 may obtain lines instead of the scan planes18, and thememory20 may store lines obtained by theprobe10 rather than the scan planes18. Thevolume scan converter42 may store lines obtained by theprobe10 rather than the scan planes18. Thevolume scan converter42 receives a slice thickness setting from a slicethickness setting control40, which identifies the thickness of a slice to be created from the scan planes18. Thevolume scan converter42 creates a data slice from multiple adjacent scan planes18. The number of adjacent scan planes18 that are obtained to form each data slice is dependent upon the thickness selected by slicethickness setting control40. The data slice is stored inslice memory44 and is accessed by avolume rendering processor46. Thevolume rendering processor46 performs volume rendering upon the data slice. The output of thevolume rendering processor46 is passed to thevideo processor50 anddisplay67.
• The position of each echo signal sample (Voxel) is defined in terms of geometrical accuracy (i.e., the distance from one Voxel to the next) and ultrasonic response (and derived values from the ultrasonic response). Suitable ultrasonic responses include gray scale values, color flow values, and angio or power Doppler information.
• FIG. 3 illustrates a method for locating and measuring a flow jet within the heart. The following example is directed to measuring the Vena Contracta which is used when evaluating Mitral Regurgitation. Instep200, ultrasound data is acquired of at least a portion of a patient's heart to image the structure of interest. For example, the ultrasound data used to measure the Vena Contracta may include data representative of the mitral valve. The ultrasound data may be a volume of data comprising 3D color Doppler data over time, such as over one or more heart cycles, and may be stored in thememory20. Alternatively, ultrasound data which has been previously acquired and stored in thememory20 may be accessed for processing.
• FIG. 4 illustrates ultrasound images displayed on thedisplay118. Volume ofdata250 acquired and/or accessed instep200 is illustrated, as well as an associatedECG trace286.Boundary lines288 and290 on theECG trace286 indicate the heart cycle being processed.
• Instep202, a first time position is selected by the operator. For example, the Vena Contracta for Mitral Regurgitation is typically measured during the systole phase of the heart cycle. The operator may scroll atime position indicator292 through theECG trace286 to select the first time position. Alternatively, thesignal processor116 may automatically detect and position thetime position indicator292 at the first time position. The operator may then adjust thetime position indicator292 after automatic positioning by thesignal processor116. It should be understood that a stand-alone computer or other processor may be used to implement the functions ofFIG. 3 in place of asignal processor116 which may be integrated with an ultrasound scanner. Further, the program instructions for implementing the functions ofFIG. 3 may be stored on various media devices known in the art.
• Instep204, the operator uses theuser interface120 to define an effective region of interest (ROI)252 around the structure or orifice of interest. For example, the operator may set a top orproximal slice plane260 at a first depth above the mitral valve or other anatomy of interest and a bottom ordistal slice plane262 at a second depth below the mitral valve to define theROI252. The proximal and distal slice planes262 and264 are parallel with respect to each other. Alternatively, thesignal processor116 may set the proximal and distal slice planes260 and262 based on predetermined or average patient data, or at preset depths. The operator may then adjust the locations of the proximal and distal slice planes260 and262. Optionally, for ease of anatomical inspection while defining theROI252, the operator may temporarily remove or turn off the color Doppler information so that only the tissue structures are displayed. In steps where the flow jet is visualized and/or measured, the color Doppler information may be turned on. Also, the operator may change the color parameters to change how the color is interpreted and displayed.
• One or more long-axis planes may also be displayed on thedisplay118 to guide the positioning of the proximal and distal slice planes260 and262. InFIG. 4, a first long-axis plane256 may show the main probe plane, or the azimuth plane, while a second long-axis plane258 may show a plane at 90 degrees to the first long-axis plane256. ADoppler ROI284 defined during the acquisition of the ultrasound data is illustrated, and the color Doppler data is calculated for ultrasound data within theDoppler ROI284. The positions of the proximal and the distal slice planes260 and262 are illustrated with first and seconddotted lines264 and265, respectively, on the first long-axis plane256 and with first and seconddotted lines266 and267, respectively, on the second long-axis plane258. Other indicators may be used. Alternatively, three long-axis planes which are 60 degrees apart with respect to each other may display standard 2D echo cardiography scanning planes with the proximal and distal slice planes260 and262 indicated thereon.
• Instep206, thevolume scan converter42 extracts multiple parallel slices from ultrasound data selected by theROI252. By way of example, two, four or six parallel slices may be extracted and displayed, although the operator may select to have more or a different number of parallel slices extracted. In one embodiment, the parallel slices may be parallel c-scan slices. In another embodiment, the parallel slices may be positioned non-orthogonal with respect to a central vector of the volumetric ultrasound scan. In another embodiment, the position of one or more of the parallel slices may be interpolated.
• FIG. 5 illustrates multiple parallel slices extracted from theROI252. The proximal and distal slice planes260 and262 are illustrated with first, second, third and fourth intermediate slice planes294,296,298 and300. First, second, third, fourth, fifth andsixth slices268,270,272,274,276 and278 are displayed on thedisplay118 ofFIG. 4. Thefirst slice268 corresponds to theproximal slice plane260 and thesixth slice278 corresponds to thedistal slice plane262, while the first through fourth intermediate slice planes294-300 correspond to the second through fifth slices270-276, respectively.
• Distance D1 between each of the adjacent slice planes260,294-300 and262 is the same, and thus the first through sixth slices268-278 are positioned equidistant relative to one another. Each of the first through sixth slices268-278 may have the same predetermined thickness. Alternatively, the operator may change the thickness of the first through sixth slices268-278 with the slicethickness setting control40.
• Instep208, the operator may adjust the distance D1 between the slice planes260,294-300 and262 along the direction of arrow A (FIG. 5), which also adjusts the size of theROI252. For example, the operator may move one or more of the first andsecond lines264 and265 displayed on the first long-axis plane256 and first andsecond lines266 and267 displayed on the second long-axis plane258. The depth of each of the proximal and distal slice planes260 and262 may be changed independently. If theproximal slice plane260 is moved upwards towards the surface of theprobe106, thedistal slice plane262 may remain in its current location while the first through fourth intermediate slice planes294-300 are adjusted to maintain the equidistant relationships with respect to each other and the proximal and distal slice planes260 and262. The first through sixth slices268-280, position of theROI252, as well as other effected indicators, are updated on thedisplay118 to reflect the current slice information and location.
• Instep210, the operator may adjust the orientation of the slice planes260,294-300 and262 so that the flow jet runs perpendicular to the planes as illustrated by viewing the first through sixth slices268-278 on thedisplay118. The orientation adjustment may be accomplished by adjusting one or more of the first andsecond lines264 and265 on the first long-axis plane256 and the first andsecond lines266 and267 displayed on the second long-axis plane258 with theuser interface120. The orientation adjustment moves the proximal and distal slice planes260 and262 and the first through fourth intermediate slice planes294-300 in unison, maintaining the equidistant relationship between them. The slice planes260,262 and294-300 may be adjusted in any direction, such as front to back and side to side as illustrated with arrows B and C onFIG. 5. The orientation adjustment is not limited to these directions, however, and the slice planes260,262 and294-300 may be adjusted in any combination of directions. As the orientation of the slice planes260,262 and294-300 is adjusted, the first through sixth slices268-278 are updated on thedisplay118 to reflect the current position. The first andsecond lines264 and265, and266 and267, position of theROI252, as well as other effected indicators, are updated on thedisplay118 to reflect the current slice information and location.
• Thesteps208 and210 may be iterative, that is, the operator may adjust the position and orientation of the slice planes260,262 and294-300 multiple times to find the best possible location and orientation to measure the flow jet of interest. Instep212, the operator may visually identify the smallest orifice on one of the first through sixth slices268-278, which corresponds to the smallest flow jet area. In this example, the smallest flow jet area is the Vena Contracta.
• Instep214, the area of the smallest orifice, or the Vena Contracta area, is measured on the slice identified instep212.FIG. 6 illustrates an example of measuring the Vena Contracta area on aslice280. In one embodiment, the operator may use theuser interface120 to trace anarea282 or use a caliper to measure a diameter of the Vena Contracta area. Alternatively, the operator may define or select one or more points and thesignal processor116 may detect the Vena Contracta area using an edge detecting or boundary defining algorithm. Optionally, the operator may choose to measure the Vena Contracta area on more than one slice at the same time position within the heart cycle to identify the smallest orifice area.
• The position of the Vena Contracta moves during the cardiac cycle due to the movement of the atrioventricular (AV) plane. Therefore, instep216, if the operator chooses to measure the Vena Contracta area at an additional time position within the cardiac cycle, flow passes to step218 where the operator selects a next time position, which may be before or after the first time position and may be within the systole phase of the heart cycle. Optionally, thesignal processor116 may automatically select the next time position and allow the operator to adjust or change the next time position. By selecting at least two different time positions within the heart cycle, the structure of interest is automatically tracked on the slices over a portion or all of the cardiac cycle. The method then returns to step204 to set and adjust the scan planes and measure the flow jet area at the next time position.
• Returning to step216, if no more calculations are to be done, the method flows to step220. Instep220, thesignal processor116 calculates intermediate positions of the Vena Contracta by interpolating between the points identified for the first, next and/or subsequent time positions. This calculation thus provides an automatic tracking of the position of the Vena Contracta. If a single time position is used, the identified data may be interpolated over the systole phase or other phase portion(s) of the cardiac cycle, or for a predetermined time period before, after or surrounding the first time position. Instep222, thesignal processor116 measures the size of the orifice or the Vena Contracta on the multiple slice planes over time based on the volumetric color Doppler data.
• The measurement of the Vena Contracta may be more fully automated by indicating, on a first parallel slice at a first position, the area of interest. This may be done by drawing an ROI or by selecting one or more points and then automatically detecting the area with thesignal processor116. Thesignal processor116 may then detect the direction of blood flow within the ROI to define the position for the slice plane relative to theprobe106. The area may then be automatically calculated, either between the first position and an identified second position, or automatically with respect to position(s) adjacent to the first position as discussed previously.
• A technical effect is using the ultrasound data to calculate the Vena Contracta area or other identified structure within the heart over time. The automated tracking of the anatomical structure in the slice positions over all or portions of the cardiac cycle allow for an accurate measurement of the flow jet. Therefore, as the size, shape and/or position of the orifice may change, the Vena Contracta can be automatically tracked and measured from multiple slices based on the volumetric color Doppler data.
• While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

Claims (20)

1. A system for presenting multiple parallel slices, comprising:

a display for displaying ultrasound data comprising 3D Doppler data over time;

a user interface for defining a proximal plane and a distal plane within the ultrasound data that are parallel to one another, the proximal and distal planes defining a region of interest (ROI); and

a signal processor for automatically extracting at least two slices based on the ultrasound data within the ROI, the at least two slices being parallel with respect to each other, the at least two slices being displayed on the display.

2. The system ofclaim 1, further comprising the display displaying at least one long-axis plane based on the ultrasound data, the display displaying the proximal plane and the distal plane on the at least one long-axis plane.

3. The system ofclaim 1, wherein the proximal plane has a first depth and the distal plane has a second depth, wherein the proximal and distal planes have a first orientation, the signal processor automatically updating the at least two slices on the display when the user interface changes at least one of the first and second depths and the first orientation.

4. The system ofclaim 1, the user interface indicating an ROI of anatomical structure on one of the at least two slices at a first time position, the signal processor measuring an area of the ROI and interpolating corresponding areas of like anatomical structure on the ultrasound data over one of a predetermined time period prior to the first time position, a predetermined time period subsequent to the first time position, and a predetermined time period having the first time position therewithin.

5. The system ofclaim 1, the user interface indicating first and second ROIs of like anatomical structure on one of the at least two slices at first and second time positions, the signal processor tracking the like anatomical structure on the ultrasound data between the first and second time positions.

6. The system ofclaim 1, the user interface indicating first and second ROIs of like anatomical structure on one of the at least two slices at first and second time positions, the signal processor measuring a first and a second flow jet area within the first and second ROIs, the signal processor interpolating flow jet area on the ultrasound data between the first and second time positions.

7. A method for displaying multiple parallel slices, comprising:

defining a region of interest (ROI) within a volume of data, the volume of data comprising volumetric color Doppler data over at least one cardiac cycle;

automatically displaying at least two slices of ultrasound data from within the ROI at a first time position; and

calculating a first flow jet area on one of the at least two slices at the first time position.

8. The method ofclaim 7, further comprising:

defining a proximal plane within the volume of data; and

defining a distal plane within the volume of data, the distal and proximal planes being parallel to one another and defining the ROI.

9. The method ofclaim 7, further comprising:

displaying a long-axis plane based on the volume of data; and

displaying first and second parallel lines on the long-axis plane, the first and second parallel lines defining the ROI.

10. The method ofclaim 7, further comprising:

changing at least one of depth, size and orientation of the ROI within the volume of data; and

automatically updating the at least two slices of ultrasound data based on a current location of the ROI.

11. The method ofclaim 7, further comprising:

measuring a second flow jet area on one of the at least two slices at a second time position, the first flow jet area and the second flow jet area indicating like anatomical structure; and

interpolating flow jet area on the ultrasound data between the first and second time positions.

12. The method ofclaim 7, further comprising defining at least one point proximate the first flow jet area, the first flow jet area being calculated automatically based on the at least one point.

13. The method ofclaim 7, wherein the at least two slices further comprising multiple parallel slices spaced equidistant with respect to each other.

14. The method ofclaim 7, further comprising interpolating the flow jet area on the ultrasound data over one of a predetermined time period prior to the first time position, a predetermined time period subsequent to the first time position, and a predetermined time period having the first time position therewithin.

15. A method for measuring a flow jet area over a portion of a cardiac cycle, comprising:

defining a region of interest (ROI) within a volume of data comprising volumetric color Doppler data over at least one cardiac cycle;

displaying on a display multiple parallel slices of ultrasound data from within the ROI;

measuring a flow jet area on a first slice at a first time position and measuring a flow jet area on a second slice at a second time position; and

interpolating the flow jet area on the ultrasound data between the first and second time positions.

16. The method ofclaim 15, further comprising defining a proximal plane and a distal plane within the ultrasound data that are parallel to one another, the proximal and distal planes defining the ROI.

17. The method ofclaim 15, further comprising:

displaying at least one long-axis plane based on the ultrasound data; and

displaying a proximal plane and a distal plane on the at least one long-axis plane to define the ROI.

18. The method ofclaim 15, further comprising:

changing at least one of a depth, a size and an orientation of the ROI; and

updating the multiple parallel slices being displayed on the display.

19. The method ofclaim 15, wherein a position of at least one of the multiple parallel slices is interpolated.

20. The method ofclaim 15, further comprising:

setting a proximal plane and a distal plane within the volume of data to define the ROI;

changing at least one of a depth and an orientation of one of the proximal and the distal planes; and

updating the multiple parallel slices based on the changing step.

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